The acetylcholine receptors of electrgplax and muscle are large complexes consisting of several putative subunits of different molecular weights. The authenticity of all of these polypeptides as subunits of the receptor as well as their functions in synaptic transmission is undetermined. To investigate these points, antibodies to the individual polypeptides of ACh receptor will be prepared and their reactions with the polypeptides of receptors from Torpedo electroplas, rat muscle, and the BC3H-1 mouse myogenic cell line will be characterized. These antisera will be used in immunohistological (indirect immunofluorescence) studies on normal and denervated rat muscle to determine if the polypeptides are synaptic membrane components. The affects of these antisera on carbamylcholine-stimulated ion flux of BC3H-1 cells will be investigated to assess the functional importance of the subunits in the cholinergic response. Mutants of BC3H-1 cells defective in one or more of the polypeptides of the receptor complex will be isolated by their resistance to complement-mediated antibody cell lysis. These mutants will be characterized immunologically and biochemically to pinpoint the molecular defect. The effects of these mutations on the cholinergic response will be investigated by the ion flux assay. Correlation of particular aspects of ACh receptor function with the molecular components that comprise the receptor complex is the goal of this project.